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Fair Value of Assets and Liabilities - Narrative (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write down of held to maturity securities | $	$ 0	$ 0
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value | $	$ 0	$ 0
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security	0	0
U.S. government agency obligation collateralized by loans guaranteed by SBA program | Available-for-sale Securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security		1

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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